a) Field of the Invention
This invention relates in general to vehicle axle assemblies and in particular to an improved structure for a spring seat and housing for such an axle assembly and a method for manufacturing same.
b) Description of Related Art
Axle assemblies are well known structures, which are in common use in most vehicles. Such axle assemblies include a number of rotatable components that transmit rotational power from an engine of the vehicle to the wheels thereof. These rotatable components are usually enclosed in protective non-rotatable housing. The housing typically includes a central carrier (which rotatably supports a differential mechanism therein) having a pair of outwardly extending tubes (which enclose the axle shafts extending from the differential to the wheels of the vehicle). In the past, the tubes have been formed from sections of hollow cylindrical steel tubes which have been welded, bolted, or otherwise secured to the carrier to form the axle housing.
The tubes of these axle housings are frequently provided with one or more additional components for various purposes. For example, it is generally desirable to provide a circumferentially extending flange about the tube near the outer end thereof to function as a mounting surface for the components of the brake for that wheel. Also, a seat is commonly provided on the tube for securing a plurality of leaf springs or similar means for resiliently connecting the frame of the vehicle to the axle housing. Lastly, it is known to provide a pad on the tube to which a bracket is welded for securing a shock absorber or similar means for dampening oscillations of the frame of the vehicle relative to the axle housing. In the past, the brake flange, the spring seat, and the shock absorber pad have all been formed from individual components which were welded, bolted, or otherwise secured to the tubes.
Conventionally, a spring seat is secured on each tube by welding. Such spring seats comprises a plate with side sections that bent at least partially around the central portion of the axle. The leg portions of each spring seat are welded to the axle tube. FIG. 1 illustrates a conventional spring seat 6 secured to an axle tube 4 by welding. A top plate 9 and leaf spring 5 are clamped to the assembly of the axle tube 4 and spring seat 6 by U-bolts 3 which pass through registering holes in the spring seat 6 and top plate 9 and are secured by washers and nuts (not shown).
It has also been found desirable to form the axle housing integrally by casting molten metal into an appropriately shaped mold. Thus, it is known to form the carrier and tubes of the axle housing from a single piece of material cast into a predetermined shape. Furthermore, it has also been found desirable to form the additional components of the axle housing (i.e., the brake flange, the spring seat, and the shock absorber pad) integrally with the tubes by casting.
FIGS. 2 and 3 illustrate a tube 10 provided with an inner end that is adapted to be secured to a carrier (not shown) of the axle housing. Additionally the tube 10 is provided with a shock absorber pad 12, a spring seat 13 and a brake flange 14, the functions of which are well known in the art. For this known axle tube, each component 10-14 is formed by casting so that these components are integrally formed as part of the tube 10.
It can be seen that known axle housing castings are inefficient because they are composed of more material than is required to accomplish the intended function. The inclusion of the additional steel material in the known axle housing forging results in unnecessary material cost and increased weight. Since cost and weight are prime considerations in the design of axle housings and other vehicle components, it would be desirable to provide an improved axle housing which meets its intended functional requirements without adding unnecessary cost or weight thereto.
This invention relates to an improved structure for an axle assembly housing and spring seat, as well as a method for manufacturing same. The housing includes a tube which is formed by casting or other appropriate methods, and the tube is provided with a brake flange, a spring seat, a shock absorber pad, and an outer end for mounting wheel bearings. In accordance with this invention, the spring seat is formed from a composite material and this composite spring seat provides a direct replacement for the current production steel forging.
The design advantages of the composite spring seat of this invention include reduced weight (i.e. 15 lbs. to 6 lbs.), roughly half the manufacturing costs associated with the convention steel forging, and reduced noise transmitivity of the composite material.
As with the steel forged spring seat, the composite spring seat is welded to the axle housing and delivered as a packaged assembly to the customer. As a result, the material selection for the composite spring seat has the following considerations; heat resistance (i.e., heat deflection temperatures in excess of about 500xc2x0 F. and arc resistance in excess of 180xc2x0 F.); high tensile and flexural strength properties in a broad temperature range (i.e., 41 ksi and 82 ksi respectively at 23xc2x0 C.); and good impact properties (i.e., 41 ft/lb). Consequently, the best material currently envisioned by the inventors is Varimat(copyright) 156-044 SMC molding compound, 60% glass, 2xe2x80x3 chop with continuous strands, longitudinally placed at xe2x85x9cxe2x80x3.
The composite part is preferably processed in a vertical press in a 4-cavity compression mold. To facilitate the welding process, there is preferably an in-mold steel insert within the composite structure. This insert is preferable placed in each cavity within the mold prior to the SMC material. The material is a thermoset material, therefore, the mold is heated, and the die is then closed deforming the material into the desired shape. While the die is in the closed position, a dwell time is required to cure the material. The die is then opened and the part is removed.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments, when read in light of the accompanying drawing.